Check the circuit breaker box to make sure there’s power to the range hood fan. Flip the circuit back on if it’s off. If you have a fuse box, make sure the fuse is intact and replace it if it’s not. Typically range hoods don’t have plugs, but if yours does, make sure the plug is firmly in the outlet.
Test the electrical current to the fan switch with an ohm meter. Look for zero resistance when the switch is on. If the switch only turns the fan on to one speed, the switch may still be the problem because it’s only getting power to part of the switch. Turn off the electrical current to the range hood and replace the switch.
Check that the fan’s motor is working with the ohm meter. Any reading other than zero indicates the motor is the problem. You can replace the motor without removing the hood in most instances.
Look for the fan’s blower connector. Not all models have one. If your vent hood does, make sure the connections are firmly in place.
Clean the filters if the fan doesn’t move the air as well as it usually does. Use warm soapy water to cut through the grease to allow air to circulate through the vent and to the fan again.
Feel the fan’s blades on the shaft carefully. Too much movement on the shaft may cause extra noise from vibration as the fan operates. Replace the fan if there is too much wear.
Determine if your vent actually takes the air outside or just re-circulates it in the room. You can usually see ductwork for a fan that has a vent. Look in the cabinet above the vent hood. If the fan is on and you feel air coming out of the front of the vents, your range hood fan isn’t set up to vent the air outside. It’s possible to add ventilation, but you have to add the ductwork that goes with it.